I designed a custom embedded board (really simple, comparable to a 80s home computer) with 64KB SRAM, video output, and LEDs in key locations illustrating the i

I designed a custom embedded board (really simple, comparable to a 80s home computer) with 64KB SRAM, video output, and LEDs in key locations illustrating the inner workings. We started at 7, playing with Forth and assembler, drawing sprites on paper and trying to make a simple platformer game. The key point here was a physical machine that does as little magic under the hood as possible, and is super slow so you can intuitively get the limitations; I also implemented step-by-step debugging and ultra slow clock mode. Then we switched to RPi, writing simple games in Python, then we made a raytracer in plain C (easy to explain and write, huge interest spike as you get magical results), then a voxel Minecraft-like prototype. Now he's 15, mostly interested in ML and graphics. As others said, it's harder to suggest something interesting for kids to make than to actually teach them. They want shiny things immediately, so you have to make sure that each step looks somewhat closer to the target. CGI and game development is a classic attraction that still seems to work. Don't worry about dumbing everything down too much; kids easily develop superficial understanding of what you're talking about, it comes handy later in the form of easier understanding of the details. And keep in mind that at 9-10 (YMMV) there's a severe shift from goal-less play towards attempts to make something practical. Which can leave the kid disappointed and disinterested if something goes wrong or the goal is too ambitious.